JP2617847B2 - AC uninterruptible power supply - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an AC uninterruptible power supply device having an inverter configuration in which the output of an engine generator is an AC input power source and a storage battery is a backup power source.

[0002]

2. Description of the Related Art Conventionally, in remote areas where there is no commercial power supply, such as mountainous areas and remote islands, various electric facilities are operated using an AC output of an engine generator as a power supply. In this case, especially for equipment that requires measures against power failure such as computer equipment,
In order to protect the equipment from a power failure due to a failure or maintenance of the generator, power is normally supplied using an AC uninterruptible power supply having an inverter configuration using a storage battery as a backup power supply.

Further, in a factory or office in a city, in order to protect computer equipment and the like from a power failure of a commercial power supply, an engine generator and an AC power supply having an inverter configuration of this kind are provided as power supply equipment. Then, when the power outage of the commercial power source extends for a long time, the same power supply as in the above-mentioned remote place using the output of the engine generator as a power source is performed.

Next, a conventional AC uninterruptible power supply of this type using an output of an engine generator as an input power will be described with reference to FIG. In the figure, 1 is an engine generator, 2 is a rectifier for converting the AC output of the generator 1 to DC,
Reference numeral 3 denotes an inverter that uses the rectified output of the rectifier 2 as a power supply, and 4 denotes an output switching unit, which is provided between the generator 1, the inverter 3 and the load 5 with switch circuits 6, 7 having an AC thyristor configuration for instantaneous switching. It is formed.

[0005] Reference numeral 8 denotes a storage battery for supplying DC as a backup power supply to the inverter 3 when the output of the generator 1 is stopped due to failure, inspection, etc., 9 denotes a charger provided between the rectifier 2 and the storage battery 8, and 10 denotes charging. And a discharge path diode provided in parallel with the vessel 9.

[0006] 11 synchronous circuit for outputting a synchronous signal synchronized with the generator 1, 12 detects the output current to power the is the load 5 a current detector. Reference numeral 13 denotes a current-voltage converter that converts a current detection signal of the current detector 12 into a voltage. 14
Is a comparator for comparing the output signal of the current-voltage converter 13 via the input resistor 15 with the output limit value of the inverter 3 set by the reference power supply 16 and outputting a switching command for the switch circuits 6 and 7. .

Reference numeral 17 denotes a control device for the entire device to which the output signals of the synchronizing circuit 11 and the comparator 14 are supplied, and an inverter control unit having a PLL circuit configuration for controlling the driving of the inverter 3 and opening / closing control of the switch circuits 6 and 7. And a charging control unit of the charger 9. And, for example, in a remote place, the generator 1
The AC power is always driven except for a failure or maintenance, and its AC output is directly supplied to an electric lamp, a power device, and the like, and is also supplied to an AC uninterruptible power supply and rectified by the rectifier 2.

Further, for example, a zero-cross point of the output of the generator 1 is detected by the synchronization circuit 11, and a synchronization signal for each zero-cross point is supplied to the control device 17. The inverter control section of the control device 17 is formed substantially as shown in the configuration of one embodiment of the present invention in FIG.

In FIG. 2, reference numeral 18 denotes an inverter control unit,
19 is a target frequency switching circuit, 20 is a crystal oscillator, 21
Is a frequency divider having a counter configuration, 22 is a frequency detector for detecting the output frequency of the inverter 3, 23 is a PLL oscillation output circuit, and outputs a target frequency signal from the switching circuit 19 and a detection signal of the frequency detector 22. The oscillation frequency of the control reference is varied digitally or analogly by the error signal and is pulled to the target frequency (synchronization frequency) to form a control signal of this frequency. Reference numeral 24 denotes a PWM inverter drive circuit which forms a PWM drive signal corresponding to the frequency of a control signal of the PLL oscillation output circuit 23 and supplies the PWM drive signal to the inverter 3.

Conventionally, the synchronous range variable section 25 shown in FIG. 2 is not provided, and there is no control output from the variable section 25 to the oscillation output circuit 23. In addition, due to failure or inspection of the generator 1 ,
When the output stops and the power supply input loses power,
The synchronization signal is not output from the path 11. At this time, in order to stably maintain the output frequency of the inverter 3 at the rated frequency, the output of the frequency divider 21 obtained by dividing the output of the crystal unit 20 is output.
The frequency of the power is the rated frequency of the generator 1, for example, 60 Hz.
In this case, 60Hz ± 1Hz near 60Hz is selected.
Is set.

Then, for example , when the output frequency of the generator 1 is 6
At the time of steady state maintained at 0 Hz + 1 Hz, the synchronous circuit 11
The period of the output synchronization signal is output from the frequency divider 21.
If the signal to be synchronized is the longest synchronous 59 Hz, the frequency divider 21
Is shorter than the cycle of the signal output from
Output of a short signal, that is, the high-frequency synchronous circuit 11
And the oscillation output circuit 23 forms a control signal using the synchronization signal as a signal of the target frequency.
The inverter drive circuit 24 drives the inverter 3 based on this control signal. With this drive, the inverter 3 converts the rectified output of the rectifier 2 into an AC output having a target frequency, and supplies the AC output to the load 5 via the switch circuit 7.

At this time, if the output current supplied to the load 5 is smaller than the output limit value of the inverter 3, the output voltage of the current-voltage converter 13 based on the detection signal of the current detector 12 becomes the output limit value of the reference power supply 16. (Threshold)
The output of the comparator 14 becomes a switching command for inverter output selection. Then, based on the switching command of the inverter output selection, the open / close control unit of the control device 17 controls the switch circuits 6 and 7 to be turned off and on.

By the way, when the load 5 is a computer load which causes load fluctuations in computer equipment or the like, at the beginning of the increase of the load, it becomes an extremely heavy load and demands excessive current feeding, but thereafter the load amount decreases. The amount of current required is also reduced. Then, particularly at the beginning of the increase in the load, the output current of the power supply device based on the request of the load 5 may exceed the output limit value of the inverter 3.

In this case, the output voltage of the current-to-voltage converter 13 becomes higher than the threshold value of the reference power supply, the output of the comparator 14 is inverted to a switching command for generator output selection, and the switch circuits 6, 7 are turned on. The output is switched to OFF, and the output switching unit 4 switches the load power supply output from the AC output of the inverter 3 to the output of the engine generator 1. By this switching, the output of the generator 1 is directly supplied to the load 5, and the power supply limitation due to the output capacity of the inverter 3 is avoided.

When the load decreases and the output current of the power supply returns below the output limit of the inverter 3, the comparator 14
Is inverted again to the switching command of the inverter output selection, the switch circuits 6 and 7 are again inverted to off and on, and the load power supply output returns to the AC output of the inverter 3. Further, by switching the switch circuits 6 and 7, the load power supply output is switched from the inverter output to the generator output in accordance with the load fluctuation.
This automatic switching of the power supply from the generator output to the inverter output is usually called an auto return.

Next, when the output of the generator 1 is stopped due to failure or inspection of the generator 1 and the input of the power supply is cut off, the synchronization signal is not output from the synchronization circuit 11 and the switching circuit 19 is automatically turned off. Then, the selection of the output of the frequency divider 21 is switched. The frequency divider 2 that divides the output of the crystal oscillator 20.
A signal of rated frequency 60 Hz ± 1 Hz of 1 is supplied to the oscillation output circuit 23 as a signal of the target frequency, and the inverter drive circuit 24 drives the inverter 3 based on this supply.

At this time, since the output of the rectifier 2 is stopped, the DC of the storage battery 8 is supplied to the inverter 3 via the diode 10 as a backup. Based on this power supply, the inverter 3 continues load power supply using the output of the storage battery 8.

[0018]

In the case of the conventional AC uninterruptible power supply, the frequency compensator is not attached to the generator 1 in terms of cost, and the output frequency of the generator 1 is as shown in FIG. The output fluctuates relatively greatly with the increase of the output, and the output frequency of the inverter 3 cannot be drawn into the output frequency of the generator 1 under heavy load.

In this case, a cross current occurs due to the auto return operation based on the difference between the output frequencies of the generator 1 and the inverter 3, and the inverter 3 is damaged or the load power supply current fluctuates to damage the load 5. Problem.

That is, the crystal oscillator 20 and the frequency divider 21
Restrictions on so that the output frequency range of the inverter 3 in the synchronization range of the oscillation output circuit 23 based on the more formation signal is 60
If the output frequency range of the generator 1 is 60 Hz ± 3 Hz, which is wider than that, if the computer load fluctuates and the load 5 becomes heavy, the switch circuit 6 of the output switching unit 4 7 is turned on and off, and the load power is switched from the inverter 3 to the generator 1.

At this time, the output frequency of the generator 1 decreases and fluctuates in accordance with the output, and in the worst case, decreases to 57 Hz. However, the output frequency of the inverter 3 decreases only to 59 Hz. And a difference occurs.

Then, when the load circuits decrease, the switch circuits 6 and 7 are turned off and on, and the load power supply returns to the inverter 3 again. At this time, based on the difference between the output frequencies of the generator 1 and the inverter 3, A cross current flows from the switch circuit 6 to the inverter 3 via the switch circuit 7, and the cross current damages the inverter 3. In addition, the load 5 may be damaged due to the current fluctuation of the load power supply caused by the occurrence of the cross current.

An object of the present invention is to prevent damage to an inverter or a load due to cross current when a load power supply output returns from an engine generator output to an inverter output by switching an output switching unit based on an auto return operation. To do.

[0024]

In order to achieve the above object, in the AC uninterruptible power supply according to the present invention, the output current of the power supply exceeds a predetermined synchronization limit below the output limit of the inverter. A synchronous range variable unit that instructs the inverter control unit to extend the synchronous range during the operation.

[0025]

In the case of the AC uninterruptible power supply of the present invention configured as described above, if the output current of the power supply increases due to a load fluctuation during the steady power supply to which the output of the engine generator is supplied, the conventional apparatus is not used. By the same automatic return operation as described above, the load power supply output is switched from the output of the inverter to the output of the engine generator only while this output current exceeds the output limit value of the inverter.

Further, while the output current of the power supply device exceeds the synchronization limit value equal to or less than the output limit value, the synchronization range of the oscillation frequency of the control reference of the inverter control unit is expanded by the enlargement command of the synchronization range variable unit. Even if the output frequency of the engine generator is greatly reduced as the output increases, the output frequency of the inverter is synchronized with the output frequency of the engine generator. Therefore, when the load amount decreases and the load power supply output returns to the output of the inverter, the output frequency of the engine generator and the output of the inverter do not shift in synchronization, and no cross current occurs due to the switching of the output switching unit. The inverter and the load are prevented from being damaged.

[0027]

EXAMPLE One example will be described with reference to FIGS. 1, the same reference numerals as those in FIG. 3 denote the same or corresponding components, and the difference from FIG. 3 is that a synchronization range variable unit 25 is added. This variable unit 25 is the comparator 2
6, an input resistor 27 and a reference power supply 28 for setting a synchronization limit value
And supplies the output signal of the comparator 26 to the PLL oscillation output circuit 23 of the inverter control unit 18 as shown in FIG.

The synchronization limit value set by the reference power supply 28 depends on the inverter 3 set by the reference power supply 16.
Is adjusted to an appropriate value which is equal to or less than the output limit value.

When the load fluctuates to a heavy load during the steady power feeding in which the output of the generator 1 is fed to the power supply device, and then returns to the steady state, the output command of the comparator 14 The output switching unit 4 operates in the same manner as the conventional device to execute an auto return, and inverts the switch circuits 6 and 7 to ON and OFF only while the output current of the power supply device exceeds the output limit value of the inverter 3. Thus, the output of the generator 1 is supplied to the load 5 as it is.

On the other hand, when the output current increases and the output voltage of the current-voltage converter 13 exceeds the synchronization limit value of the reference power supply 28, the comparator 26 instructs the oscillation output circuit 23 to extend the synchronization range. Then, the oscillation output circuit 23 to which this command is supplied is, for example, the input allowable range of the error voltage is expanded and the change range of the oscillation frequency with respect to the error voltage is 60 Hz.
Spread from ± 1 Hz to 60 Hz ± 3 Hz.

Therefore, even if the output frequency of the generator 1 decreases to 57 Hz as the output increases, the oscillation frequency of the output oscillation circuit 23 changes to the output frequency of the generator 1 based on the synchronization signal of the synchronization circuit 11. Synchronously, the frequency drops to 57 Hz, and the output frequency of the inverter 3 matches the output frequency of the engine generator 1.

Then, since the synchronization limit value is set to be equal to or less than the output limit value, the output current of the power supply returns to or less than the output limit value of the inverter 3, and the switch circuits 6, 7 are turned off and on again by the auto return operation. When the load power supply output is reversed to return to the output of the inverter 3, the output frequencies of the generator 1 and the inverter 3 do not deviate, and a cross current unlike the conventional device does not occur. Is prevented from being damaged. Note that the output frequency range of the generator 1 and the synchronization range of the oscillation output circuit 23 are not limited to the embodiment.

Further, the configuration of the inverter control unit 18 and the method of expanding the output frequency of the inverter 3 based on the command to expand the synchronization range of the comparator 26 are not limited to the embodiments. The present invention can be applied not only to an AC uninterruptible power supply used in a remote place, but also to an AC uninterruptible power supply such as a factory or an office in a city where the power supply of the generator 1 is performed only during a long-time blackout of a commercial power supply. Of course.

[0034]

Since the present invention is configured as described above, the following effects can be obtained. If the output current of the power supply increases due to load fluctuations during the steady power supply in which the output of the engine generator 1 is supplied, the output current exceeds the output limit value of the inverter 3 by the auto return operation similar to the conventional device. Only during this time, while the load power supply output is switched from the output of the inverter 3 to the output of the generator 1, while the output current of the power supply device exceeds the synchronization limit value equal to or less than the output limit value, 25, the synchronizing range of the oscillation frequency of the control reference of the inverter control unit 18 is expanded, and even if the output frequency of the generator 1 decreases as its output increases, the output frequency of the inverter 3 decreases. Synchronizes with the output frequency of

Therefore, when the load amount decreases and the load power supply returns to the output of the inverter 3, the output frequencies of the generator 1 and the inverter 3 do not shift in synchronization with each other. Does not occur, the inverter 3 and the load 5 can be prevented from being damaged, and a highly reliable AC uninterruptible power supply can be provided.

[Brief description of the drawings]

FIG. 1 is a block diagram of an AC uninterruptible power supply according to an embodiment of the present invention.

FIG. 2 is a detailed block connection diagram of a part of FIG. 1;

FIG. 3 is a block connection diagram of a conventional device.

FIG. 4 is a relationship diagram between an output of an engine generator and a frequency.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Engine generator 2 Rectifier 3 Inverter 4 Output switching part 8 Storage battery 18 Inverter control part 25 Synchronization range variable part

 ────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hideki Imai 2-14-3 Awaji, Higashiyodogawa-ku, Osaka City Sansha Electric Manufacturing Co., Ltd.

Claims (1)

(57) [Claims] 1. A rectifier for rectifying an AC output of an engine generator, an inverter to which a rectified output of the rectifier is supplied, a backup storage battery for supplying power to the inverter when the AC output fails, and a load for supplying to a load. An output switching unit that switches the load power supply output from the inverter output to the AC output only while the output current exceeds the output limit value of the inverter, and an oscillation frequency of a control reference is set by a synchronization signal synchronized with the AC output. An AC uninterruptible power supply, comprising: an inverter control unit that controls the frequency of the AC output within the synchronized range and controls the output frequency of the inverter to the oscillation frequency. The output current is equal to or less than the output limit value. A synchronization range variable unit that instructs the inverter control unit to extend the synchronization range while exceeding a predetermined synchronization limit value AC uninterruptible power supply, characterized in that it comprises.